Amino acid derivatives and their therapeutical applications

ABSTRACT

Compounds having the properties of morphinic substances, particularly  anasia, with beneficial effects on behaviour and with peripheral effects without their major drawbacks (tolerence, addiction), the blood-brain barrier and having the following formula : 
     
         H.sub.2 
    
      N--CH(R 1 )--CH(R 2 )--S--S--CH(R 3 )--CH(R 4 )--A--B--Z 
     wherein: AB preferably represents a CO amide bond, R 2  et R 3  preferably represent a hydrogen atom, R 1  et R 4  preferably represent, independently of each other, a benzyl grouping, --CH 2  CH 2  SCH 3 , --CH 2  --CH 2  --S(O)--CH 3  or --CH 2  --CH(CH 3 )  2 , Z may represent a --CH(R 5 )[CH(R 6 )] n  --COO(R 7 ) grouping wherein: R 5  may represent a hydrogen atom, a methyl grouping, a benzyl grouping or a phenyl grouping, R 6  may represent a hydrogen atom and may also form a hydrocarbon cycle with R 5 , or Z may represent a heterocyclic grouping, and preferably a morpholinyl grouping. No drawings.

PRIOR APPLICATION

This application is a continuation of U.S. patent application Ser. No. 835,961 filed as PCT/FR90/00627, Aug. 23, 1990, now abandoned.

The invention relates to novel amino acid derivatives, to a method for preparing them and to their therapeutical applications.

It is known that natural opioid peptides or enkephalins are essentially degraded by two enzymes belonging to the metallopeptidase class, neutral endopeptidase EC 3.4 24.11 (enkephalinase) which cuts the Gly-Phe⁴ bond (Malefroy et al., Nature, 27.6, 523, (1978)) and chiefly aminopeptidase N EC 3.4 11.2 which cuts the Tyr¹ -Gly² bond (Waksman et al. Eur. J. Pharm., 117, 233 (1985)).

Dipeptide derivatives having activity with respect to enkephalinase (Roques et al.), Nature, 288 286 (1980), French Patent 80/08,601) as well as compounds which inhibit aminopeptidase N (Chan., Biochem. Biophys. Res. Commun. 116 (1983) 297; Chan et al., J. Biol. Chem. 257 (1982) 7955) are known. Similarly, mixed inhibitors of the different enkephalinase activities have been described (Fournie-Zaluski) et al. J. Med. Chem. 28 (1989) 1158; French Patent 86/13,413). Compared to molecules which selectively inhibit neutral endopeptidase or aminopeptidase, these mixed inhibitors display more potent pharmacological properties. However, these compounds which possess a hydroxamate function are very poor at crossing the blood-brain barrier, and hence display considerable analgesic properties only after intracerebroventricular (i.c.v.) injection.

One of the objectives of the invention is to provide novel compounds capable of jointly inhibiting both of the enzymatic activities responsible for the degradation of enkephalins, and of manifesting their pharmacological properties after intravenous (i.v.), subcutaneous (s.c.) or oral (per os) injection.

Another objective of the invention is to provide novel compounds derived from amino acids which display some properties of morphinic substances, especially analgesia, beneficial effects on behavior (sedation, euphoria, reward) and peripheral effects (antidiarrheal, antitusive, hypotensive, anti-inflammatory, etc.) without having their major drawbacks (tolerance, addiction, etc.).

The novel compounds according to the present invention do not possess a hydroxamate function, but are characterized by a disulfide bond.

Moreover, the novel compounds are capable of jointly inhibiting both of the endogenous enkephalin-degrading enzymes or of potentiating the action of exogenously administered analogs.

The subject of the invention is, more especially, compounds corresponding to the formula (I).

    H.sub.2 N--CH(R.sub.1)--CH(R.sub.2)--S--S--CH(R.sub.3)--CH(R.sub.4)--A--B--Z (I)

in which: R₁ represents:

- a saturated or unsaturated, linear or branched hydrocarbon chain containing from 1 to 6 carbon atoms, unsubstituted or substituted with a group OR in which R is a hydrogen, a linear or branched C1 to C4 hydrocarbon chain or a phenyl (Phe) or benzyl residue; a thioether group SR, R having the same definition as above, or an oxidized thioether group S(O)R, R having the same definition as above,

- a methylcycloalkyl group containing 5 to 6 carbon atoms, a benzyl or phenyl group, optionally substituted:

with 1 to 5 halogen, in particular fluorine, atoms,

or with a group OR' or SR', R' being an alkyl group having 1 to 4 carbon atoms, the thioether SR' being oxidized or otherwise on the sulfur atom,

or with an amino group optionally mono- or disubstituted with an aliphatic alkyl group having 1 to 6 carbon atoms, oxidized or otherwise on the amine function,

- a methylene group substituted with an aromatic or saturated heterocycle containing 5 or 6 carbon atoms, possessing as the hereto atom a nitrogen atom, an oxygen atom or a sulfur atom, the nitrogen and sulfur atoms optionally being oxidized in the form of N-oxide or S-oxide. R₂ independently represents a hydrogen atom or a methyl group. R₃ represents a hydrogen atom or a linear or branched alkyl chain. R₄ represents:

- a saturated or unsaturated, linear or branched hydrocarbon chain containing from 1 to 6 carbon atoms, unsubstituted or substituted with a hydroxyl group, an ether group OR in which the group R has the same meaning as above, a thiol SH, thioether SR group (R having the same meaning as above) or a thioether group oxidized to sulfoxide,

- a methylcycloalkyl group having 5 to 6 carbon atoms, a benzyl or phenyl group, optionally substituted with 1 to 5 halogen, in particular fluorine, atoms, with a hydroxyl or a thiol, an ether or a thioether OR' or SR', R' having from 1 to 4 carbon atoms, the thioether being oxidized or otherwise on the sulfur atom, with an amino group optionally mono- or disubstituted with an aliphatic alkyl group having 1 to 6 carbon atoms, oxidized or otherwise on the amine function,

- a methylene group substituted with an aromatic or saturated heterocycle containing 5 or 6 carbon atoms, possessing as the hetero atom a nitrogen atom, an oxygen atom or a sulfur atom, the nitrogen and sulfur atoms optionally being oxidized in the form of N-oxide or S-oxide. Z can represent:

* a group --CH(R₅)--[CH(R₆)]_(n) --COO(R₇) in which R₅ and R₆ can represent, independently of one another:

a hydrogen,

a linear or branched alkyl group having 1 to 6 carbon atoms, unsubstituted or substituted with hydroxyl or ether OR, thiol SH or thioether SR groups (R having the definition specified above),

- a phenyl (Phe) or benzyl group unsubstituted or substituted with 1 to 5 halogen atoms; a group OR' or SR', R' having the definition specified above. R₅ and R₆ can also each represent saturated or unsaturated hydrocarbon chains containing from 1 to 6 carbon atoms in which 1 to 2 carbon atoms may be substituted by an oxygen, sulfur or nitrogen atom, capable of forming one or more saturated or aromatic 5- to 6-membered hydrocarbon rings or saturated or aromatic 5- to 6-membered heterocyclic rings. n can be equal to 0 or 1. R₇ represents:

a hydrogen,

or a saturated or unsaturated, linear or branched hydrocarbon group having 1 to 6 carbon atoms,

or a benzyl group.

* a morpholinyl group N--C₄ --H₈ O

* piperidyl group --N--C₅ H₁₀ optionally substituted with an --OH residue, a --CO₂ H residue, a residue COOR¹ in which R¹ represents a linear or branched alkyl chain containing 1 to 6 carbon atoms, a phenyl residue or a benzyl residue.

* a pyrazolinyl group --N--C₄ H₈ --NH, a substituted pyrazolinyl group --NC₄ H₈ --N--R² in which R² represents an alkyl chain containing from 1 to 6 carbon atoms, a benzyl residue or a phenyl residue. A--B represents an amide CONH or retro-amide NHCO group.

The compounds of formula (I) have from 2 to 6 asymmetric carbon atoms. They hence exist in the form of racetalc mixtures and in the forms of enantiomers, of diastereoisomers or of stereoisomers. The subject of the invention is also the addition salts of the compounds of formula (I), obtained with pharmacologically acceptable organic or inorganic acids, such as the hydrochloride, hydrobromide, sulfates, nitrates, borates, phosphates, methanesulfonate, acetate, fumarate, succinate, ascorbate, oxalate, lactate, pyruvate, citrate, tartrate, maleate, malonate, benzoate, salicylate, 2,6-dichlorobenzoate, trimethoxybenzoate, diaminobenzenesulfonate, chromoglycate, benzenesulfonate, cyclohexanesulfonate, toluenesulfonate, dipropylacetate, glucose 1-phosphate, pamoate and palmitate.

Preferably, the compounds according to the invention are such that, in the formula (I), if Z represents a group --CH(R₅)--[CH(R₆)]_(n) --COO--(R₇).

R₂ and R₃ represent hydrogen atoms,

AB represents an amide link CONH,

R₁ represents a --CH₂ CH₂ S(O) CH₃ group, and

R₇ represents a --CH₂ Phe group, in which case they can correspond to the formulae: ##STR1## and if R₄ represents a --HC₂ CH₂ S(O)CH₃ group, they can correspond to the formulae: ##STR2##

The compounds according to the invention can also preferably correspond to the formulae: ##STR3##

The latter compounds are especially advantageous on account of their properties of bioavailability (active administered orally).

The subject of the invention is, moreover, a method for preparing the compounds of formula (I) defined above in which Z represents a group --CH(R₅)--[CH(R₆)]_(n) --CO(R₇) comprising the following steps:

compounds of formula (II):

    R.sub.8 NH--CH(R.sub.1)--CH(R.sub.2)SH

in which R₈ represents a group protecting group for the amine function, are condensed with dithiodipyridine (III) ##STR4## to yield the compounds of general formula (IV): ##STR5## the compound (IV) is then condensed with the compounds of formula (V):

    HS--CH(R.sub.3)--CH(R.sub.4)--A--B--CH(R.sub.5)--[CH(R.sub.6).sub.n --COO(R.sub.7)                                            (V)

to yield the compounds of the formula (VI):

    R.sub.8 NH--CH(R.sub.1)--CH(R.sub.2)--S--S--CH(R.sub.3)--CH(R.sub.4)--A--B--CH(R.sub.5)--[CH(R.sub.6)].sub.n --COO(R.sub.7)

the amine function of the compound (VI) is then deprotected to yield the compound of formula (I).

Preferably, the condensation of the compound of formula (II) with dithiopyridine (III) is performed at room temperature in the presence of acetic acid in ethanol.

The condensation of the intermediate compound (IV) with the compound (V) is performed in ethanol at room temperature.

The intermediate products (II) and (V) are synthesized according to the procedures described in the literature (Chan, Biochem. Biophys. Res. Commun., 116, 297, (1983) and Cushman et al., Biochemistry, 16, 5484, (1977)).

The protective group R₈ is preferably t-butyloxy carbonyl (t. Boc). This group may be removed using trifluoroacetic acid in methylene chloride.

If R₂ represents a hydrogen atom, the product of formula (II) may be obtained from a beta-amino alcohol of formula:

    H.sub.2 N--CH--(R.sub.1)--CH.sub.2 OH                      (VII)

- by protection of the amine function using a group R₈, resulting in the formation of the product of formula:

    R.sub.8 NH--CH(R.sub.1)--CH.sub.2 OH                       (VIII)

then by activation of the alcohol function, in particular in the form of rosylate, resulting in the formation of a product of formula:

    R.sub.8 NH--CH(R.sub.1) CH.sub.2 OT.sub.S                  (IX)

in which T_(S) represents a rosylate group,

- then by conversion of the tosylate group to an acetylthio group, resulting in the formation of the product of formula:

    R.sub.8 NH--CH(R.sub.1)--CH.sub.2 --S--COCH.sub.3          (X)

- then by alkaline hydrolysis of the product (X) in a reducing atmosphere, resulting in the formation of the compound of formula (II).

The beta-amino alcohol products of formula (VII) are obtained by a protocol described in the literature [(Chan. Biochem. Biophys. Res. Commun. 116 297 (1983)].

If R₂ represents a hydrogen atom, the product of formula (X) may be obtained from the product of formula (VIII) under the conditions of the Mitsunobu reaction (Synthesis (1981), 1-28), that is to say in the presence of triphenylphosphine and a dialkyl azodicarboxylate.

If R₂ represents a --CH₃ group and if R₁ and R₄ have the same meaning, the compound of formula (II) may be prepared by a Curtius rearrangement (Patai, The Chemistry of Azides groups, 397, (1971)) from a compound of formula:

    CH.sub.3 --CO--SCH(CH.sub.3)CHR.sub.1 --CO.sub.2 H         (XI)

by treatment of said compound with sodium azide NaN₃ in the presence of dicyclohexylcarbodiimide (DCC), resulting in the formation of the product of formula:

    CH.sub.3 --CO--SCH(CH.sub.3)CHR.sub.1 --CON.sub.3          (XII)

then by heating in the presence of an alcohol, resulting in the formation of the product of formula:

    CH.sub.3 --CO--SCH(CH.sub.3)CHR.sub.1 --NHR.sub.8          (XIII)

then by acid hydrolysis of the acetylthio group under reducing conditions.

Preferably, the amine function of the compound (XIII) is protected in the form of carbamate.

If R₃ represents a hydrogen atom or a --CH₃ group, and AB an amide group CONH, the compound of formula (V) may be obtained from a compound of formula:

    CH.sub.3 --CO S CH(R.sub.3)CH(R.sub.4)--CO.sub.2 H         (XIV)

which are 2-substituted (acetylthio)propanoic (sic) acids (Cushman et al. (1977), Biochemistry 16 5484).

- by alkaline hydrolysis of said compound, preferably under oxidizing conditions, resulting in the formation of the compound of formula:

    (SCH(R.sub.3)CH(R.sub.4)--CO.sub.2 H).sub.2                (XV)

followed by condensation under conventional conditions of peptide coupling with an amino ester of formula:

    H.sub.2 N--CH(R.sub.5)--[CH(R.sub.6)].sub.n --CO--OR.sub.7 (XVI)

resulting in the formation of a compound of formula:

    (S CH(R.sub.3)CH(R.sub.4)CONH CH(R.sub.5)[CH(R.sub.6).sub.n ]--COOR.sub.7).sub.2                                      (XVII)

followed by treatment in a reducing medium (zinc and hydrochloric acid).

The beta-amino acids of formula (XVI) are synthesized by conventional methods (Xie et al. , J. Med. Chem. (1989), 32, 1497).

The compound of formula XI may be obtained from the phosphorus ylide of formula:

    (Phe).sub.3 P--CH(R.sub.1)--COO--CH.sub.3                  (XVIII)

by Witting condensation with acetaldehyde, resulting in the formation of the compound of formula:

    CH.sub.3 CH═C(R.sub.1)--CO--)CH.sub.3                  (XIX)

then by alkaline hydrolysis, resulting in the formation of the compound of formula:

    CH.sub.3 CH═C(R.sub.1)CO.sub.2 H                       (XX)

then by addition of thioacetic acid.

If R₃ represents a hydrogen atom or a --CH₃ group and if R₁ and R₄ have the same meaning and if AB represents a retro-amide group NHCO, the compound of formula (V) may be prepared, respectively, from the compounds (X) and (XlII) corresponding to the general formula:

    CH.sub.3 CO--S--CH(R.sub.2)CH(R.sub.1)NHR.sub.8            (XXI)

by alkaline hydrolysis under oxidizing conditions, resulting in the formation of the compound of formula:

    [SCH(R.sub.2)CH(R.sub.1)NMR.sub.8 ].sub.2                  (XXII)

then by deprotection of the amine function, yielding the compound of formula:

    [SCH(R.sub.2)CH(R.sub.1)NH.sub.2 ].sub.2                   (XXIII)

then by condensation under conventional conditions of peptide coupling with malonic or succinic acid monoesters of formula:

    CO.sub.2 H--CH(R.sub.5)--[CH(R.sub.6)].sub.n --COOR.sub.7  (XXIV)

resulting in the formation of a compound of formula:

    [SCH(R.sub.2)CHR.sub.1 --NHCO--CHR.sub.5 --(CHR.sub.6).sub.n --COOR.sub.7 ].sub.2

then by treatment in a reducing medium.

The malonic or succinic acid monoesters of formula (XXIV) are synthesized by conventional methods (Fournie-Zaluski et al., Int. J. Pept. Prot. Res., 33, (1989), 146).

The subject of the invention is, in addition, a method for preparing the compounds of formula I in which the group Z represents:

* a morpholinyl group N--C₄ H₈ O

* a piperidyl group --N--C₅ H₁₀ optionally substituted with an --OH residue, a --CO₂ H residue, a residue COOR¹ in which R¹ represents a linear or branched alkyl chain containing 1 to 6 carbon atoms, a phenyl residue or a benzyl residue.

* a pyrazolinyl group --N--C₄ H₈ --NH, a substituted pyrazolinyl group --NC₄ H₈ --N--R² in which R² represents an alkyl chain containing from 1 to 6 carbon atoms, a benzyl residue or a phenyl residue characterized in that compounds of formula

    (SCH(R.sub.3)CH(R.sub.4)--CO.sub.2 H).sub.2                (XV)

are condensed with a hydrazine of formula

    H.sub.2 N--Z                                               (XXV)

resulting in the formation of a compound of formula

    (SCH(R.sub.3)CH(R.sub.4)--CONH--Z).sub.2                   (XXVI)

which is condensed with a compound of formula ##STR6## to yield the compound of formula (I).

Another subject of the invention is a pharmaceutical composition containing at least one compound as defined above, or obtained by the method as defined above, in combination with one or more compatible or pharmaceutically acceptable diluents or adjuvants.

These compositions may be used, in particular, as a major analgesic, as an antalgic and as an anti-depressant. These compounds are almost devoid of the side effects of morphinics (tolerance and addiction). Their main application is hence in the field of analgesia and antidepressants.

Another subject of the invention is the application of the compounds as defined above, or obtained by a method as defined above, as medicinal products.

The invention will be further illustrated, without being in any way limited, by the examples below:

The list of compounds prepared according to Examples 1 to 32 is given in Table I.

For all the compounds described in this table, R₂ and R₃ both represent hydrogen atoms, R₇ represents a --CH₂ Phe group and AB an amide link CONH.

                                      TABLE I                                      __________________________________________________________________________     Example                                                                              R.sub.1  R.sub.4  R.sub.5     R.sub.6                                    __________________________________________________________________________      1    CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.2 Phe                                                                            H           --                                          2    CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.2 Phe                                                                            CH.sub.3    --                                          3    CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.2 Phe                                                                            CH.sub.2 Phe                                                                               --                                          4    CH.sub.2 Phe                                                                            CH.sub.2 Phe                                                                            H           --                                          5    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 Phe                                                                            H           --                                          6    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 Phe                                                                            CH.sub.3    --                                          7    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 Phe                                                                            CH.sub.2 Phe                                                                               --                                          8    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 Phe                                                                            H           --                                          9    CH.sub.2 SCH.sub.3                                                                      CH.sub.2 Phe                                                                            H           --                                         10    CH.sub.2 S(O)CH.sub.3                                                                   CH.sub.2 Phe                                                                            H           --                                         11    CH.sub.2 SCH.sub.2 Phe                                                                  CH.sub.2 Phe                                                                            H           --                                         12    CH.sub.2 S(O)CH.sub.2 Phe                                                               CH.sub.2 Phe                                                                            H           --                                         13    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         14    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         15    CH.sub.2 SCH.sub.3                                                                      CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         16    CH.sub.2 S(O)CH.sub.3                                                                   CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         17    CH.sub.2 SCH.sub.2 Phe                                                                  CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         18    CH.sub.2 S(O)CH.sub.2 Phe                                                               CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         19    CH.sub.2 St Bu                                                                          CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         20    CH.sub.2 S(O)tBu                                                                        CH.sub.2 CH(CH.sub.3).sub.2                                                             CH.sub.3    --                                         21    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.3    --                                         22    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.3    --                                         23    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 Phe                                                                            Phe         H                                          24    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 Phe                                                                            Phe         H                                          25    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 Phe                                                                            CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2              26    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 Phe                                                                            CH.sub. 2 --CH.sub.2 --CH.sub.2 --CH.sub.2             27    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 CH.sub.2 SCH.sub.3                                                             Phe         H                                          28    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          Phe         H                                          29    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 Phe                                                                               H                                          30    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 Phe                                                                               H                                          31    CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 CH.sub.2 SCH.sub.3                                                             CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2              32    CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 CH.sub.2 S(O)CH.sub.3                                                          CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2              __________________________________________________________________________

EXAMPLE 1 Preparation of H₂ N--CH[CH₂ CH(CH₃)₂ ]--CH₂ --S--S--CH₂ CH (CH₂ Phe)CONH--CH₂ COOCH₂ Phe

Step 1 Preparation of ##STR7##

A solution of 1.6 g of Boc--NH--CH[CH₂ --CH(CH₃)₂ ]--CH₂ --SH in 5 ml of outgassed ethanol is added to a solution of 3 g of 2,2'-dithiodipyridine in 5 ml of out-gassed ethanol and 0.35 ml of acetic acid, and the mixture is stirred for 24 h at room temperature. It is evaporated to dryness. A yellow oil is obtained, which is chromatographed on silica gel in a 9:1.25:0.25 cyclohexane/ethyl acetate/acetic acid mixture. 1.62 g of the expected product are obtained. Yld 72%; Rf (8:2 cyclohexane/ethyl acetate)=0.25

Step 2 Preparation of Boc--NH--CH--[CH₂ CH(CH₃)₂ ]CH₂ --S--S--CH₂ CH (CH₂ Phe)--CONH--CH₂ --COO--CH₂ Phe

A solution of 1.7 g of N-(2-mercaptomethyl-3-phenyl-1-oxopropylglycine benzyl ester in 10 ml of outgassed ethanol is added to a solution of 1.6 gof the above compound in 10 ml of outgassed ethanol. The mixture is stirredfor 24 h at room temperature. It is evaporated to dryness. A yellow oil is obtained, chromatographed on silica gel with a 7:3:0.5 cyclohexane/EtOAc/AcOH mixture as eluent.

2.42 g (Yld 86%) of the expected product are obtained. Rf (8:2:0.5 cyclohexane/ethyl acetate/acetic acid)=0.38.

Step 3 Preparation of the final product

2.4 g of the above compound are dissolved in 4 ml of CH₂ Cl₂ ·6 ml of trifluoroacetic acid (TFA) are added at 0° C. Themixture is stirred for 2 h at 0° C. and 2 h at room temperature. It is evaporated to dryness. It is chromatographed on silica gel using a 20: 1 CH₂ Cl₂ /MeOH mixture as eluent. 1.63 g of the expected product are obtained (Yld 80%). Rf (9:1 CH₂ Cl₂ /MeOH)=0.46.

EXAMPLE 2 Preparation of H₂ N--CH(CH₂ CH(CH₃)₂)CH₂ --S--S--CH₂ --CH--(CH₂ Phe)CONH--CH (CH₃)COOCH₂ Phe

Starting with 0.685 g of 2-boc-amino-4-methyl-1-pentyl-1'-dithiopyridine prepared in Example 1, step 1, and 0.715 g of N-[2-mercaptomethyl-3-phenyl-1-oxopropyl]alanine benzyl ester, and according to the conditions of Example 1, step 2, the protected inhibitor (0.88 g, 75%) is obtained. After deprotection, the expected compound (0.57g, 80%) is obtained in the form of an oily product, Rf (8:2:0.5 cyclohexane/EtoAC/AcOH)=0.39. Mass spectrum CI, NH₃ (M+1)=489.

EXAMPLE 3 Preparation of H₂ N--CH(CH₂ CH(CH₃)₂)CH₂ --S--S--CH₂ --CH--(CH₂ Phe)COHN--CH (CH₂ Phe))COO--CH₂Phe

Starting with 0.685 g of 2-boc-amino-4-methyl-1-pentyl-1'-dithiopyridine prepared in Example 1, step 1, and 0.870 g of N-[2-mercaptomethyl-3-phenyl-1-oxopropyl]phenylalanine benzyl ester, and according to the conditions of Example 1, step 2, the protected inhibitor (0.90 g, 60%) is obtained. After deprotection, the expected compound (0.554 g, 72%) is obtained, Rf (8:2:0.5 cyclohexane/EtoAC/AcOH)=0.41. Massspectrum CI, NH₃ (M+1)=565.

EXAMPLE 4 Preparation of H₂ N--CH(CH₂ Phe)CH₂ --S--S--CH--CH(CH₂ Phe)--CONH--CH--COOCH₂ Phe

Step 1 Preparation of ##STR8##

Starting with 410 mg of 2,2'-dipyridyl disulfide and 250 mg of 2-t-Boc-amino-3-phenyl-1-propanethiol, and following the working conditions of Example 1, 170 mg (Yld 42%) of the expected product are obtained in the form of an oil. Rf (9:10:0.5 cyclohexane/EtoAC/AcOH)=0.26.

Step 2 Preparation of t-Boc-NH-CH(CH₂ Phe)--CH₂ S--S--CH₂ CH--(CH₂ Phe)--CONH--COO--CH ₂ Phe

Starting with 170 mg of the above compound and 160 mg of N-(2-mercaptomethyl-3-phenyl-1-oxopropyl)-glycine benzyl ester, and following the experimental conditions of Example 1, 174 mg (61%) of the expected product are obtained in the form of an oil: Rf (7:3:0.5 cyclohexane/EtoAC/AcOH)=0.54.

Step 3 Preparation of the final product

Starting with 170 mg of the above compound, and following the experimental conditions of Example 1, 80 mg (Yld 55%) of the expected product are obtained in oily form. Rf (9:1CH₂ Cl₂ /MeOH)=0.56.

EXAMPLE 5 Preparation of H₂ N--CH(CH₂ CH₂ SCH₃)--CH₂ --S--S--CH₂ --CH (CH₂ Phe)--CONH--CH₂ Phe

Step 1 Preparation of ##STR9##

Starting with 0.82 g of 2-t-Boc-amino-4-mercaptomethyl-1-butanethiol and 1.43 g of 2,2'-dipyridyl disulfide, and following the procedure of Example1, 0.77 g (Yld 68%) of the expected product is obtained in the form of an oil. Rf (8:2:0.5 cyclohexane/Et/AOc/AcOH)=0.32.

Step 2 Preparation of t-Boc--NH--CH(CH₂ --CH₂ --S--CH₃)-CH₂ --S--S--CH₂ CH (CH₂ Phe)CONH--CH₂ --COO--CH₂ Phe

Starting with 0.75 g of the above compound and 0.76 g of N-(2-mercaptomethyl-3-phenyl-1-oxopropyl)-glycine benzyl ester, and following the experimental conditions of Example 1, 1.18 g (Yld 87%) of the expected product are obtained in the form of an oil. Rf (cyclohexane/EtoAc/AcOH (8.2:0.5)=0.46.

Step 3 Preparation of the final product

Starting with 0.4 g of the above compound, and using the experimental conditions of Example 1, 0.35 g of the expected product (Yld 85%) is obtained in the form of, an oil. Rf (9:1CH₂ Cl₂ /MeOH)=0.50.

EXAMPLE 6 Preparation of H₂ N--CH(CH₂ CH₂ SCH₃)CH₂ --S--S--CH₂ --CH(CH₂ Phe)CONH--CH (CH₃)COOCH₂ Phe

Starting with 0.9 g of 2-boc-amino-4-mercaptomethyl-1-butyl-1'-dithiopyridine prepared in Example1, step 1, and 0.88 g of N-[2-mercaptomethyl-4-phenyl-1-oxopropyl]alanine benzyl ester, and according to the conditions of Example 1, step 2, the protected inhibitor (1.07 g, Yld 70%) is obtained. After deprotection according to the method of Example 1, step 3, 0.66 g (75%) of the expectedproduct is obtained. Rf (9:1:0.5 CH₃ /MeOH/AcOH)=0.62. Mass. Spectrum CI, NH₃ (MH)=501.

EXAMPLE 7 Preparation of H₂ N--CH(CH₂ CH₂ SCH₃)CH₂ --S--S--CH₂ --CH--(CH₂ Phe) --CONH--CH₂ --CH₂ --Phe)--COOCH₂ Phe.

Starting with 0.7 g of 2-boc-amino-4-mercaptomethyl-1-butyl-1'-dithiopyridine prepared in Example1, step 1, and 0.9 g of N-[2-mercaptomethyl-3-phenyl-1-oxopropyl]phenylalanine benzyl ester, and according to the conditions of Example 1, step 2, the protected inhibitor (08 g, Yld 60%) is obtained. After deprotection according to the method ofExample 1, step 3, 0.616 g (72%) of the expected product is obtained. Rf (9:1:0.5 CHCl₃ /MeOH/AcOH)=0.65 and 0.75. Mass spectrum CI, NH₃ (M+1)=583.

EXAMPLE 8 Preparation of H₂ N-CH(CH₂ CH₂ S(O)CH₃)--CH₂ S--S--CH₂ --CH(CH₂ Phe) CONH--CH₂ COOCH₂ Phe

This compound is obtained from the compound of Example 5, protected on the amine function (step 2). Oxidation of 0.5 g of this compound with sodium periodate (1 eq) in an aqueous-alcoholic medium enables 0.380 g of the corresponding sulfoxide, which is an oily product, to be obtained. Rf (7:3:0.5 cyclohexane/EtoAC/AcOH)=0.20 (Yld 78%).

Treatment with trifluoroacetic acid in the same manner as in step 3 of Example 1 enables the expected final compound to be liberated. M=0.289 g (Yld 85%) Rf (9:1CH₂ Cl₂ /MeOH)=0.25.

EXAMPLE 9 Preparation of H_(b) 2 N--CH(CH₂ SCH₃)CH₂ --S--S--CH₂ --CH(CH₂ Phe) --CONHCH₂ --COOCH₂ Phe

Step 1 Preparation of ##STR10##

Starting with 2.2 g of 2-(N-t-Boc-amino)-1-mercapto-3-(methylthio)propane, and under the conditions of Example 1, step 1, 2.3 g of the expected product (70%) are obtained, RE (8:2 cyclohexane) EtOAc)=0.28.

Step 2 Preparation of t-Boc NHCH (CH₂ SCH₃)CH₂ --S--S--CH₂ --CH(CH₂ Phe) CONHCH₂ COOCH₂ Phe

Starting with 2.2 g of the above compound, and under the conditions of Example 1, step 2, 3.07 g (82%) of the expected product are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.52.

Step 3 Preparation of the final product

Starting with 3 g of the above compound, and under the conditions of Example 1, step 3, 1.99 g of the expected compound (Yld 78%) are obtained - Rf (9:1 CH₂ Cl₂ /MeOH) - 0.38.

EXAMPLE 10 Preparation of H₂ N--CH(CH₂ CH₂ S(O)CH₃)--CH₂ --S--S--CH₂ --CH--(CH2Phe) --CONHCH₂ --COOCH₂ Phe

This compound is obtained from the final compound of Example 9, protected on the amine function, (step 2). Oxidation under the conditions of Example9 yields the corresponding sulfoxide (Yld 45%) Rf (7:3:0.5 cyclohexane/EtoAC/AcOH)=0.30.

Treatment with TFA (conditions of Example 1, step 3) liberates the expectedcompound. Rf (7:3 CH₂ Cl₂ /MeOH)=0.35 (Yld 80%).

EXAMPLE 11 Preparation of H₂ N--CH(CH₂ SCH₂ Phe)CH₂ S--S--CH₂CH(CH₂ Phe)--CONHCH₂ --COOCH₂ Phe

Step 1 Preparation of ##STR11##

Starting with 1.48 g of 2-(N-t-Boc-amino)-1-mercapto-3-(benzylthio)propane,and under the conditions of Example 1, step 1, 1.3 g (Yld 68%) of the expected product are obtained. Rf (7:3 cyclohexane/EtOAc)=0.31.

Step 2 Preparation of t-Boc NH--CH(CH₂ SCH₂ Phe)CH₂ --S--S--CH₂ --CH (CH₂ Phe)CONH--CH₂ COO--CH₂ Phe

Starting with 1.38 g of the above compound, and under the conditions of Example 1, step 2, 1.73 g (Yld 80%) of the expected compound are obtained.Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.55.

Step 3 Preparation of the final compound

Starting with 1.7 g of the above compound, and under the conditions of Example 1, step 3, 1.04 g (70%) of the expected product are obtained. Yld (8:2 CH₂ Cl₂ /MeOH)=0.43.

EXAMPLE 12 Preparation of H₂ N--CH(CH₂ S(O)CH₂ Phe)--CH₂ --S--S--CH₂ CH--(CH₂ Phe)--CONHCH₂ COOCH₂ Phe

This compound is obtained from the compound of Example 11, protected on theamine function (step 2). Oxidation under the conditions of Example 8 leads to the corresponding sulfoxide Yld (70%) Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.32

Treatment with TFA (Example 1, step 3) liberates the expected compound Rf (7:3 CH₂ Cl₂ /MeOH)=0.48 (Yld 82%).

EXAMPLE 13 Preparation of H₂ NCH(CH₂ CH₂ SCH₃)CH₂ S--S--CH₂ CH(CH₂ CH--(CH₃)₂) CONHCH(CH₃)COOCH₂ Phe

1.7 g of the compound obtained in Example 5, step 1, is condensed under theconditions of Example 1, step 2, with 1.6 g of benzyl N-(2-mercaptomethyl-4-methyl-1-oxopentyl)alaninate. 1.94 g (Yld 70%) of the final compound, protected on the amine function, are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.41.

Treatment with TFA (Example 1, step 3) liberates the expected final compound (1.35 g) (Yld 83%) Rf (8:2 CH₂ Cl₂ /MeOH) 0.51.

EXAMPLE 14 Preparation of H₂ NCH(CH₂ CH₂ S(O)CH₂ SSCH₂ CH(CH₂ CH(CH₃)₂ --CONHCH(CH₃) COOCH₂ Phe

The compound of Example 13, protected on the amine function, is oxidized under the conditions described for Example 8. After deprotection with TFA (Example 1, step 3), the expected inhibitor is obtained. Overall Yld 60%. Rf (8:2 CH₂ Cl₂ /MeOH)=0.36.

EXAMPLE 15 Preparation of H₂ N--CH(CH₂ SCH₃)CH₂ S--S--CH₂ CH--(CH₂ CH(CH₃)₂)--CONH (CH₃)COOCH₂ Phe

1.65 g of the compound (Example 9, step 1) is condensed under the conditions of Example 1, step 2, with 1.6 g of benzyl N-(2-mercaptomethyl-4-methyl-1-oxopentyl)alaninate. 1.89 g (Yld 70%) of the compound protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.45.

Treatment with TFA (Example 3, step 1) liberates the final compound (1.32 g) (Yld 82%) Rf (8:2 CH₂ Cl₂ /MeOH)=0.60.

EXAMPLE 16 Preparation of H₂ N--CH(CH₂ S(O)CH₃)CH₂ S--S--CH₂ CH--(CH₂ CH--(CH₃) ₂)--CONHCH(CH₃)COOCH₂ Phe

The compound of Example 15, protected on the amine function, is oxidized under the conditions described for Example 8. After deprotection with TFA (Example 1, step 3), the expected final compound is obtained. Overall Yld 55%. Rf (8:2 CH₂ Cl₂ /MeOH)=0.38

EXAMPLE 17 Preparation of H₂ NCH(CH₂ SCH₂ Phe]CH₂ S--S--CH₂ CH--(CH₂ CH--(CH₃)₂)--CONHCH (CH₃)COOCH₂ Phe

The compound (Example 11, step 1) (1 g) is condensed under the conditions of Example 1, step 2, with 1.07 g of benzyl N-(2-mercaptomethyl-4-methyl-1-oxopentyl)alaninate. 1.34 g (Yld 65%) of the final compound protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.42. Treatment with TFA (Example 1, step3) liberates the final compound (0.99 g) (Yld 86%) Rf (8:2 CH₂ Cl₂ /MeOH)=0.35.

EXAMPLE 18 Preparation of H₂ N--CH(CH₂ S(O)CH₂ Phe)CH₂ S--S--CH₂ CH--(CH₂ CH(CH₃) ₂)--CONHCH(CH₃)COOCH₂ Phe

The final compound of Example 17, protected on the amine function, is oxidized under the conditions described for Example 8. After deprotection with TFA (Example 1, step 3), the expected final compound is obtained. Overall Yld (73%) Rf (7:3 CH₂ Cl₂ /MeOH)=0.52.

EXAMPLE 19 Preparation of H₂ N--CH(CH₂ StBu)CH₂ S--S--CH₂ CH--(CH₂ CH (CH₃)₂)--CONHCH(CH₃)COOCH₂ Phe

Starting with 0.93 g of t-Boc-S-t·butylcysteinethiol, and under the conditions of Example 1, step 1, 1.06 g (Yld 80%) of the correspondingdisulfide are obtained. This compound is then condensed under the conditions off Example 1, step 2, with 0.86 g of benzyl N-(2-mercaptomethyl-4-methyl-1-oxopentyl)alaninate. 1.19 g of the protected final compound (Yld 75%) are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.31. Treatment with TFA liberates the final compound (0.84 g) (Yld 85%) Rf (7:3 CH₂ Cl₂ /MeOH)=0.38.

EXAMPLE 20 Preparation of H₂ N--CH(CH₂ S(O)tBu)CH₂ S--S--CH₂ CH--(CH₂ CH(CH₃)₂)CONHCH(CH₃) COOCH₂ Phe

The compound of Example 19, protected on the amine function, is oxidized under the conditions described for Example 8. After deprotection with TFA (Example 1, step 3), the expected final compound is obtained. (Overall Yld68%) Rf (7:3 CH₂ Cl₂ /MeOH)=0.30.

EXAMPLE 21 Preparation of H₂ NCH(CH₂ CH₂ SCH₃)CH₂ --S--S--CH₂ --CH--(CH₂ CH₂ SCH₃) --CONHCH(CH₃)COOCH₂ Phe

1.71 g of the disulfide (Example 5, step 1) is condensed under the conditions of Example 1, step 2, with 1.70 g of benzyl N-(2-mercaptomethyl-4-methylmercapto-1-oxobutyl)alaninate. 2.1 g (72%) of the final compound protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH) 0.58. Treatment with TFA (Example 1, step3) liberates the final compound (1.18 g) (Yld 68%) Rf (7:3 CH₂ Cl₂ /MeOH): 0.42.

EXAMPLE 22 Preparation of H₂ N--CH(CH₂ CH₂ S(O)CH₃)CH₂ --S--S--CH₂ --(CH₂ CH₂ S(O) CH₃)CONHCH(CH₃)COOCH₂ Phe

The final compound of Example 21, protected on the amine function, is oxidized under the conditions described for Example 8. After deprotection with TFA (Example 1, step 3), the expected final compound is obtained. Overall Yld 56%.

EXAMPLE 23 Preparation of H₂ NCH(CH₂ CH₂ SCH₃)CH₂ --S--S--CH₂ --CH--(CH₂ Phe) CONH--CH(Phe)CH₃ COOCH₂ Phe

1.19 g of the disulfide (Example 5, step 1) is condensed under the conditions of Example 1, step 2, with 1.44 g of benzyl N-(2-mercaptomethyl-3-phenyl-1-oxopropyl)3-phenyl-beta-alaninate. 1.59 g (Yld 70%) of the final compound protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH): 0.28. Treatment with TFA (Example 1, step 3) liberates the final compound (1.15 g) (Yld 85%) Rf (7:3 CH₂ Cl₂ /MeOH)=0.60.

EXAMPLE 24 Preparation of H₂ NCH(CH₂ CH₂ S(O)CH₃)CH₂ --S--S--CH₂ CH--(CH₂ Phe)CONHCH(Phe)CH₂ COOCH₂ Phe

The final compound of Example 23, protected on the amine function, is oxidized under the conditions described for Example 8. After deprotection with TFA (Example 1, step 3), the expected final compound is obtained. (Overall Yld 58%). Rf (7:3 CH₂ Cl₂ /MeOH)=0.25.

EXAMPLE 25 Preparation of ##STR12##

0.895 g of the disulfide (Example 5, step 1) is condensed under the conditions of Example 1, step 2, with 1.027 g of benzyl 2-[N-(2-mercaptomethyl-3-phenyl-1-oxopropyl)amino]-cyclohexanecarboxylate.1.12 g (Yld 68%) of the final product protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.32. Treatment with TFA (Example 1, step 3) liberates the final compound (0.78 g) (Yld 82%) Rf (7:3 CH₂ Cl₂ /MeOH): 0.63.

EXAMPLE 26 Preparation of ##STR13##

The final compound of Example 25, protected on the amine function, is oxidized under the conditions described in Example 8. After deprotection with TFA, (Example 1, step 3), the expected compound is obtained. Overall Yld 62%. Rf (8:2 CH₂ Cl₂ /MeOH)=0.28.

EXAMPLE 27 Preparation of H₂ N--CH(CH₂ CH₂ SCH₃)--CH₂ --S--S--CH₂ --CH--(CH₂ CH₂ SCH₃)--CONH--CH(Phe)--CH₂ --COOCH₂ Phe

1.1 g of the disulfide (Example 5, step 1) are condensed under the conditions of Example 1, step 2, with 1.39 g of benzyl 3-[N-(2-mercaptomethyl-4-methylmercapto-1-oxobutyl)amino]-phenyl-propanoate. 1.44 g (Yld 65%) of the final compound protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.42. Treatment with TFA(Example 1, step 3) liberates the final compound (1.01 g) (Yld 85%) Rf (7:3CH₂ Cl₂ /MeOH): 0.72.

EXAMPLE 28 Preparation of H₂ N--CH(CH₂ CH₂ S(O)CH₃)CH₂ --S--S--CH₂ --CH(CH₂ --CH₂ --S (O)CH₃)CONH--CH(Phe)--CH₂ --COOCH₂ Phe

The final compound of Example 27, protected on the amine function, is oxidized under the conditions described in Example 4. After deprotection with TFA (Example 1, step 3), the expected compound is obtained. Overall Yld 53%. Rf (8:2 CH₂ Cl₂ /MeOH)=0.35.

EXAMPLE 29 Preparation of H₂ N--CH(CH₂ CH₂ SCH₃)CH₂ --S--S--CH₂ --CH(CH₂ CH₂ --SCH₃)--CONH--CH(CH₂ Phe)--CH₂ --COOCH₂ Phe

0.83 g of the disulfide (Example 5, step 1) is condensed under the conditions of Example 1, step 2, with 1.07 g of benzyl 3-[N-(2-mercaptomethyl-4-methylmercapto-1-oxobutyl)amino]-4-phenylbutanoate. 1.22 g (72%) of the final compound protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.41. Treatment with TFA (Example 1, step 3) liberates the final compound (0.79 g) (Yld 72%) Rf (7:3 CH₂ Cl₂ /MeOH): 0.70.

EXAMPLE 30 Preparation of H₂ N--CH(CH₂ S(O)CH₃)--CH₂ --S--S--CH₂ --CH[CH₂ --CH₂ S(O) CH₃ ]CONH--CH(CH₂Phe)--CH₂ --COOCH₂ Phe

The final compound of Example 29, protected on the amine function, is oxidized under the conditions of Example 8. After deprotection with TFA (Example 1, step 3), the expected compound is obtained. Overall Yld 68%. Rf (8:2 CH₂ Cl₂ /MeOH)=0.33.

EXAMPLE 31 Preparation of ##STR14##

0.95 g of the disulfide (Example 5, step 1) is condensed under the conditions of Example 1, step 2, with 1.13 g of benzyl 2-[N-(2-mercaptomethyl-4-methylmercapto-1-oxobutyl)amino]cyclohexanecarboxylate. 1.43 g (78%) of the final product protected on the amine function are obtained. Rf (7:3:0.5 cyclohexane/EtOAc/AcOH)=0.39. Treatment with TFA(Example 1, step 3 ) liberates the final compound (0.88 g) (Yld 75%) Rf (7:3 CH₂ Cl₂ /MeOH): 0.65.

EXAMPLE 32 Preparation of ##STR15##

The compound protected on the amine function of Example 31 is oxidized under the conditions of Example 8. After deprotection with TFA (Example 1,step 3), the expected compound is obtained. Overall Yld 58%. Rf (8:2 CH₂ Cl₂ /MeOH)=0.30.

EXAMPLE 33 Preparation of ##STR16##

The compound protected on the amine function of Example 5, step 1, is condensed with N-morpholinyl (isopropylmethyl)-3-mercaptopropanamide underthe conditions of Example 5, step 2. The compound obtained is then oxidizedwith sodium periodate and is thereafter deprotected with trifluoroacetic acid under the conditions of Example 8 to yield the final compound. Overall yield: 62%. Rf (8:2 CH₂ Cl₂ /MeOH)=0.12.

EXAMPLE 34 Biological activity of the compounds according to the invention

The biological activity relates to the inhibition of purified aminopeptidase N and of purified neutral endopeptidase.

1) In vitro inhibition of enkephalinase activities.

a) Inhibitory potency against neutral endopeptidase

The inhibitory power is determined on purified rabbit kidney neutral endopeptidase following the protocol described in the literature (Blumberget al. Life Sci. (1981) 28, 301). After a preincubation for 15 minutes at 25° C., an aliquot of proteins is incubated for 20 minutes at 25° C. in the presence of 20 nmol of (³ H)-D-Ala² -Leu⁵ -enkephalin and the test compound in solution in Tris-HCl buffer (pH 7.4) in the presence of dithiothreitol DTT (100 equivalents relative to the inhibitor). The reaction is stopped by adding 0.2 N HCl. The tritiated metabolite (³ H)-Tyr-D-Ala-Gly is separated from the D-Ala² -Leu⁵ -enkephalin by chromatography on a Porapak column, and the quantity formed measured using a liquid scintillation counter.

b) Inhibitory potency against aminopeptidase N

The inhibitory power is measured on purified porcine kidney aminopeptidase (Boehringer, France). The assay is performed in a manner identical to the above, using (³ H)-Leu⁵ -enkephalin as a substrate. The metabolite formed, (³ H)-Tyr, is separated by chromatography on a Porapak column, and the quantity formed measured using a liquid scintillation counter.

The activity of the different compounds is expressed as 50% inhibitory concentrations (IC₅₀), and the results are summarized in Table II.

                  TABLE II                                                         ______________________________________                                                   IC.sub.50    IC.sub.50                                                         Neutral endopeptidase                                                                       Aminopeptidase N                                        ______________________________________                                         Final compound of                                                                          2*10.sup.-9 M  5*10.sup.-9 M                                       Example 1                                                                      Final compound of                                                                          2.5*10.sup.-9 M                                                                               5*10.sup.-9 M                                       Example 2                                                                      Final compound of                                                                          1.2*10.sup.-9 M                                                                               5*10.sup.-9 M                                       Example 3                                                                      Final compound of                                                                          2*10.sup.-9 M  8*10.sup.-9 M                                       Example 4                                                                      Final compound of                                                                          2*10.sup.-9 M  2*10.sup.-9 M                                       Example 5                                                                      Final compound of                                                                          1.2*10.sup.-9 M                                                                               2*10.sup.-9 M                                       Example 6                                                                      Final compound of                                                                          2.5*10.sup.-9 M                                                                               2*10.sup.-9 M                                       Example 7                                                                      Final compound of                                                                          2*10.sup.-9 M  2*10.sup.-9 M                                       Example 8                                                                      Final compound of                                                                          7*10.sup.-9 M  2*10.sup.-9 M                                       Example 22                                                                     Final compound of                                                                          5*10.sup.-9 M  2*10.sup.-9 M                                       Example 26                                                                     Final compound of                                                                          3*10.sup.-9 M  2*10.sup.-9 M                                       Example 28                                                                     Final compound of                                                                          3*10.sup.-9 M  2*10.sup.-9 M                                       Example 30                                                                     Final compound of                                                                          4*10.sup.-9 M  2*10.sup.-9 M                                       Example 32                                                                     Final compound of                                                                          5*10.sup.-9 M  2*10.sup.-9 M                                       Example 33                                                                     ______________________________________                                    

Identical inhibitory powers are obtained against these two enzymes after incubation of the compounds with rat brain membrane fractions in place of dithiothreitol.

2) "In vivo" inhibition of cerebral NEP

The enzymatic activity of cerebral NEP is compared in mice untreated or treated with a given dose of compound (approximately 2.5 mg/kg injected intravenously. The animals are sacrificed at variable times after injection of the inhibitor, and the NEP activity is determined in the brain by measuring the degradation of (³ H)-D-Ala² -Leu⁵ -enkephalin.

For the final compound of Example 1, injected at a dose of 2.7 μmol/kg (47.6 μg in 100 μl), the following results are obtained:

    ______________________________________                                         time         % inhibition cerebral NEP                                         ______________________________________                                          15' (n = 4) 96 ± 9                                                          60' (n = 4) 68 ± 4                                                         120' (n = 4) 63 ± 2                                                         180' (n = 4)  42 ± 16                                                       ______________________________________                                    

For the final compound of Example 7, the following are obtained under the same conditions:

    ______________________________________                                         time         % inhibition cerebral NEP                                         ______________________________________                                          60' (n = 4) 96 ± 5                                                         120' (n = 5) 96 ± 4                                                         180' (n = 5) 92 ± 4                                                         ______________________________________                                    

EXAMPLE 35 Pharmacological study of the compounds

a) Acute toxicity

Determination of the mortality in mice is observed following a single intravenous administration of increasing doses of the test compounds. The LD₅₀ for all the compounds studied is greater than 100 mg/kg i.v.

b) Antalgic activity

1) Hot .plate test: This involves the licking and jumping reflex of the mouse on a plate heated to 55° C., according to the method of Jacobet al (Arch Int. Pharmacodyn. 122 287, 1959; 1961).

1.1. Administered i.v. (100 μl in tail vein) in mice, the compounds tested display a characteristic effect both on the latency time of jumpingand on latency time of licking. These effects are antagonized by naloxone (0.5 mg/kg s.c.).

The results are expressed in Table III as a % analgesia. The percentage analgesia is expressed for each dose of compound tested by the following formula: ##EQU1##

                  TABLE III                                                        ______________________________________                                         Compound       50% analgesia                                                                              50% analgesia                                       ______________________________________                                         Final compound of                                                                             4 mg/kg     20 mg/kg                                            Example 1                                                                      Final compound of                                                                             2.5 mg/kg   10 mg/kg                                            Example 5                                                                      Final compound of                                                                             5 mg/kg     15 mg/kg                                            Example 7                                                                      Final compound of                                                                             2.5 mg/kg   10 mg/kg                                            Example 8                                                                      Final compound of                                                                             4.5 mg/kg   25 mg/kg                                            Example 22                                                                     Final compound of                                                                             8 mg/kg     30 mg/kg                                            Example 26                                                                     Final compound of                                                                             4 mg/kg     15 mg/kg                                            Example 28                                                                     Final compound of                                                                             3 mg/kg     15 mg/kg                                            Example 30                                                                     Final compound of                                                                             2 mg/kg     10 mg/kg                                            Example 32                                                                     ______________________________________                                    

1.2 Administered i.p. in mice, the test compounds display a characteristic effect on the times of restraint of jumping and of licking. These effects are antagonized by naloxone (0.5 mg/kg).

    ______________________________________                                         Compound of Example 1  10    mg/kg                                             Compound of Example 5  7     mg/kg                                             Compound of Example 7  8     mg/kg                                              Compound of Example 22                                                                               6     mg/kg                                              Compound of Example 32                                                                               5.5   mg/kg                                             ______________________________________                                    

2) Test on abdominal cramps

(Hendershot and Forsaith. J. Pharmacol. (1975), 125, 237): This test measures the number of cramps induced by i.p. injection of 100 μl of a 0.02% solution of phenylbenzoquinone. The number of cramps is counted during 10 minutes, 10 minutes after the injection. Administered i.v., the compounds decrease the number of cramps.

    ______________________________________                                                         dose     % analgesia                                           ______________________________________                                         Final compound of Example 1                                                                      1 mg/kg    24.6% ± 8                                      Final compound of Example 1                                                                      3 mg/kg    46.9% ± 7.9                                    Final compound of Example 1                                                                      9 mg/kg    73.9% ± 8.2                                    Final compound of Example 7                                                                      2.5 mg/kg  32% ± 4                                        Final compound of Example 7                                                                      5 mg/kg    68% ± 9                                        Final compound of Example 7                                                                      10 mg/kg   95% ± 4                                        ______________________________________                                    

3) Test of withdrawal of the tail in rats: (tail flick test): administered i.v. in rats, the compounds according to the invention produce a significant extension of the time of withdrawal of the tail. These effectsare antagonized by naloxone (0.5 mg/kg s.c.).

The results are expressed as a % analgesia for the same dose (10 mg/kg) of all the compounds tested.

    ______________________________________                                                          % analgesia                                                   ______________________________________                                         Compound of Example 1                                                                             20%                                                         Compound of Example 5                                                                             25%                                                         Compound of Example 7                                                                             42%                                                          Compound of Example 32                                                                           36%                                                         ______________________________________                                    

c) Potentiation of the behavioral effects (locomotor hyperactivity) inducedby the compounds according to the invention after long-term treatment with antidepressants:

1 h after i.v. or p.o. administration in rats, the compounds according to the invention induce an increase in locomotor activity. This effect is considerably increased after long-term treatment with neuroleptics such assulpiride (100 mg/kg i.p. every day). This potentiation is not apparent until three weeks after the beginning of the treatment with neuroleptics. The results show an increase in the concentration of endogenous enkephalins, in agreement with the results obtained with morphine by Stinus et al. (psychoparmacology, 85, 323, (1985).

    ______________________________________                                         Results*             Locomotor activity**                                      ______________________________________                                         control rat***       100%                                                      rat treated i.v. with the compound                                                                  400%                                                      of Example 5 (5 mg/kg)                                                         rat treated i.v. with the compound                                                                  400%                                                      of Example 7 (3 mg/kg)                                                         rat treated i.v. with the compound                                                                  350%                                                      of Example 30 (2 mg/kg)                                                        rat treated i.v. with the compound                                                                  370%                                                      of Example 30 (20 mg/kg)                                                       ______________________________________                                         *after three weeks of longterm treatment with sulpiride                        **measured by the number of righting movements                                 ***corresponds to animals given longterm treatment with sulpiride but whic     did not receive an inhibitor.                                             

d) Mice despair test

This test, described by Porsolt et al. (Arch. Int. Pharmacodyn. Ther, 299, 327 (1977), enables the antidepressant properties of the claimed compoundsto be evaluated.

Mice are treated with increasing doses of the compounds thirty minutes before the test, and the immobility of the animals is measured relative tocontrols which receive only the vehicle. The immobility time is decreased by the compounds according to the invention, and this effect is antagonized by naloxame (0.5 mg/kg s.c.).

    ______________________________________                                         Results               Immobility time (s)                                      ______________________________________                                         controls              165 ± 15                                              mouse treated with compound Ex. 5                                                                    108 ± 12*                                             (5 mg/kg i.p.)                                                                 mouse treated with compound Ex. 30                                             (2 mg/kg i.p.)        96 ± 8*                                               (20 mg/kg p.o.)       101 ± 10*                                             ______________________________________                                         *p < 0.01.                                                                

e) Study of the tolerance and addiction effects induced by long-term administration of the compound of Example 8:

1) The compound 8 is administered s.c. four times per 24 hours at a dose of5 mg/kg for 6 days to mice and at 10 mg/kg to rats.

Morphine (hydrochloride) is administered under the same conditions (0.5 mg/kg in mice, 2 mg/kg in rats). The control animals receive only the vehicle.

    ______________________________________                                         Results in % analgesia relative to the controls                                            days                                                                           0        1         6                                               ______________________________________                                         mouse/morphine                                                                               100 ± 10                                                                                60 ± 10                                                                              0                                           rat/morphine   70 ± 12                                                                                20 ± 3                                                                               0                                           mouse/compound 8                                                                             100 ± 10                                                                               100 ± 8                                                                               70 ± 15                                  rat/compound 8                                                                               40 ± 5   40 ± 5                                                                               30 ± 7                                   rat/compound 7                                                                               100 ± 10                                                                               100 ± 8                                                                               80 ± 10                                  ______________________________________                                    

2) After long-term treatment for 6 days under the conditions described above, the rats undergo an injection of 2 mg/kg of naloxane s.c. The signsof abstinence syndrome are measured according to Cowan et al. (J. Pharmacol. Exp. Ther. (1988) 246, 950).

Compared to morphine, long-term treatment with the compound 8 gives rise tovery weak addiction effects, illustrated by the absence of jumps, absence of fall in temperature and absence of hair loss which are the most severe signs of a habituation crisis.

3) Injection i.v. of the compound 7 into an animal (mouse or rat) which is morphine-tolerant leads to an analgesic response identical to that obtained in a control animal. This demonstrates the absence of cross-tolerance between morphine and the compound 7.

The subject of the invention is, moreover, methods for the treatment of depression and pain, in which effective quantities of at least one of the compounds described above are administered to the individual to be treated. The administration routes suited to said methods are those commonin these types of treatment, especially the intravenous, oral, subcutaneonsor intraperitoneal route. 

We claim:
 1. A compound of the formula

    H.sub.2 N--CH(R.sub.1)--CH(R.sub.2)--S--S--CH(R.sub.3)--CH(R.sub.4)--A--B--Z

in which R₁ is saturated or unsaturated, linear or branched hydrocarbon chain containing from 1 to 6 carbon atoms, unsubstituted or substituted with =OR in which R is hydrogen, a linear or branched C1 to C4 hydrocarbon chain or phenyl or benzyl; =SR, R having the same definition as above, or an oxidized thioether group S(O)R, R having the same definition as above, methylcycloalkyl of 5 to 6 carbon atoms, benzyl or phenyl optionally substituted:with 1 to 5 halogen, or OR' or SR', R' being an alkyl group having 1 to 4 carbon atoms, =SR' being optionally oxidized on the sulfur atom, or with an amino group optionally mono- or disubstituted with an aliphatic of 1 to 6 carbon atoms, optionally oxidized on the amine, R₂ is hydrogen or methyl, R₃ is hydrogen or a linear or branched alkyl chain, R₄ is saturated or unsaturated, linear or branched hydrocarbon chain containing from 1 to 6 carbon atoms, unsubstituted or substituted with a hydroxyl group, =OR in which R has the same meaning as above, =SH, =SR thioether group oxidized to sulfoxide, or a methylcycloalkyl group having 5 to 6 carbon atoms, a benzyl or phenyl group, optionally substituted with 1 to 5 halogen, with a hydroxyl or a thiol, =OR' or =SR', R' being alkyl of 1 to 4 carbon atoms, the thioether being optionally oxidized on the sulfur atom, with an amino group optionally mono- or disubstituted with an aliphatic of 1 to 6 carbon atoms, optionally oxidized on the amine function, Z is --CH(R₅)--CH(R₆)_(n) --COO(R₇) in which R₅ and R₆ are individually selected from the group consisting of hydrogen,alkyl group having 1 to 6 carbon atoms, unsubstituted or substituted with hydroxyl or =OR, =SH or =SR groups, or a phenyl (Phe) or benzyl unsubstituted or substituted with 1 to 5 halogen atoms; =OR' or =SR', R' having the definition specified above, R₅ and R₆ can also each represent saturated or unsaturated hydrocarbon chains containing from 1 to 6 carbon atoms in which 1 to 2 carbon atoms may be substituted by an oxygen, sulfur or nitrogen atom, capable of leading to the formation of one or more saturated or aromatic 5- to 6-membered hydrocarbon rings,n is 0 or 1, R₇ is selected from the group consisting of hydrogen, saturated or unsaturated, linear or branched alkyl group having 1 to 6 carbon atoms and benzyl, A--B represents an amide CONH or retro-amide NHCO in the forms of racemic mixtures or in the form of enantiomers, of diastereoisomers or of stereoisomers, as well as mixtures thereof and their non-toxic, pharmaceutically acceptable salts.
 2. Compounds according to claim 1 characterized in that Z is

    --CH(R.sub.5)--(CH(R.sub.6)).sub.n --COO(R.sub.7)

R₂ and R₃ both are hydrogen, AB is an amide link COHN, R₁ is --CH₂ CH₂ S(O)CH₃ and R₇ is benzyl.
 3. Compounds according to claim 2, characterized in that R₄ represents --CH₂ --CH₂ S(O)CH₃.
 4. Compound according to claim 2, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)--CH.sub.2 S--S--CH.sub.2 --CH(CH.sub.2 Phe)CONHCH.sub.2 COOCH.sub.2 Phe


5. Compound according to claim 2, corresponding to the formula: ##STR17##
 6. Compound according to claim 3, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)CH.sub.2 --S--S--CH.sub.2 CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)CONHCH (CH.sub.3)--COOCH.sub.2 Phe.


7. Compound according to claim 3, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)CONHCH (Phe)--CH.sub.2 --COOCH.sub.2 Phe.


8. Compound according to claim 3, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)CONHCH (CH.sub.2 Phe)--CH.sub.2 COOCH.sub.2 Phe.


9. Compound according to claim 3, corresponding to the formula: ##STR18##
 10. Compound according to claim 1, corresponding to the formula:

    H.sub.2 NCH(CH.sub.2 CH.sub.2 SCH.sub.3)CH.sub.2 S--S--CH.sub.2 CH(CH.sub.2 CH(CH.sub.3).sub.2)CONHCH(CH.sub.3) COOCH.sub.2 Phe.


11. Compound according to claim 1, corresponding to the formula:

    H.sub.2 NCH(CH.sub.2 CH.sub.2 SCH.sub.3)CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 CH.sub.2 SCH.sub.3)CONHCH(CH.sub.3) COOCH.sub.2 Phe.


12. Compound according to claim 1, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH(CH.sub.3).sub.2)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 Phe)CONH--CH.sub.2 COOCH.sub.2 Phe.


13. Compound according to claim 1, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH(CH.sub.3).sub.2)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 Phe)CONH--CH(CH.sub.3) COOCH.sub.2 Phe.


14. Compound according to claim 1, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH(CH.sub.3).sub.2)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 Phe)CONH--CH(CH.sub.2 Phe) --COOCH.sub.2 Phe.


15. Compound according to claim 1, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 SCH.sub.3)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 Phe)CONH--CH.sub.2 --COOCH .sub.2 Phe.


16. Compound according to claim 1, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 SCH.sub.3)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 Phe)CONH--CH(CH.sub.3) COOCH.sub.2 Phe.


17. Compound according to claim 1, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 SCH.sub.3)CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 Phe)CONH--CH(CH.sub.2 Phe) COOCH.sub.2 Phe.


18. Compound according to claim 1, corresponding to the formula:

    H.sub.2 N--CH(CH.sub.2 CH.sub.2 S(O)CH.sub.3)--CH.sub.2 --S--S--CH.sub.2 --CH(CH.sub.2 Phe)--CONH--CH (CH.sub.2 Phe)--COOCH.sub.2 Phe.


19. A method of relieving pain in warm-blooded animals comprising administering to warm-blooded animals an analgesically effective amount of a compound of claim
 1. 20. An analgesic composition comprising an analgesically effective amount of a compound of claim 1 and an inert pharmaceutical carrier. 